JP2008174402A - Die for molding glass substrate, method of manufacturing glass substrate, method of manufacturing glass substrate for information recording medium, and method of manufacturing information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a die for producing a glass substrate to be used in an information recording medium by press-molding molten glass, wherein the die can suppress sticking of a glass substrate when it is released from the die to prevent development of break and cracks of the glass substrate. <P>SOLUTION: The die for molding a glass substrate comprises a lower die having a first molding surface for receiving molten glass and an upper die having a second molding surface for pressurizing the molten glass between the second molding surface and the first molding surface. At least one of the first molding surface and the second molding surface is convex, and the gap distance between the first molding surface and the second molding surface at the time of pressurizing the molten glass is minimum at a position becoming as the center of the glass substrate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a glass substrate molding die for producing a glass substrate used for an information recording medium by press molding molten glass, a method for producing a glass substrate using the molding die, and the production method. The present invention relates to a method for manufacturing a glass substrate for an information recording medium using a glass substrate and a method for manufacturing an information recording medium.

  Among information recording media having a recording layer utilizing properties such as magnetism, light, and magnetomagnetism, a typical example is a magnetic disk. Conventionally, aluminum substrates have been widely used as magnetic disk substrates. However, in recent years, with the demand for a reduction in the flying height of the magnetic head for improving the recording density, the surface smoothness is superior to that of an aluminum substrate and the surface defects are few, so that the flying height of the magnetic head can be reduced. The proportion of using glass substrates as magnetic disk substrates is increasing.

  Such a glass substrate for an information recording medium such as a magnetic disk is manufactured by subjecting a glass substrate called a blank material to polishing. A method for producing a glass substrate by press molding, a method for producing a glass substrate by cutting a plate glass produced by a float method, and the like are known. Among these methods, a method of producing a glass substrate by directly press-molding molten glass is attracting attention because it can be expected to have particularly high productivity.

  However, in the method of producing a glass substrate by press molding, after the press molding with the upper and lower molds, the molded glass substrate strongly sticks to the mold, and the glass substrate is broken at the time of mold release, There was a problem that cracks may occur.

In the method of press molding by heating and softening a glass material, not by the method of press molding molten glass, and molding the glass substrate, an inert gas or the like is supplied from a through hole with a diameter of about 1 mm provided in the upper mold. A method of releasing the glass substrate has been proposed (see, for example, Patent Document 1).
JP 2002-187727 A

  However, the method of directly press-molding molten glass to produce a glass substrate is characterized in that the viscosity of the glass at the start of pressing is very low compared to the method of press-molding by heating and softening a glass material. . Therefore, if a mold having a through-hole as described above is used in a method for producing a glass substrate by directly press-molding molten glass, the molten glass enters the through-hole, resulting in a convex portion on the glass substrate, and polishing. There is a problem that extra time and labor are required for the subsequent processes. In addition, there is a problem that the glass that has entered the through-hole is a starting point, and the glass substrate is easily cracked or cracked.

  The present invention has been made in view of the technical problems as described above, and an object of the present invention is to provide a glass substrate molding die for producing a glass substrate used for an information recording medium by press molding molten glass. In other words, it is to provide a glass substrate molding die capable of suppressing the sticking of the glass substrate at the time of mold release and preventing the glass substrate from cracking or cracking. Furthermore, another object of the present invention is to provide a method for producing a glass substrate using the mold for molding a glass substrate, a method for producing a glass substrate for an information recording medium using the glass substrate produced by the production method, and an information recording medium. It is to provide a manufacturing method.

  In order to solve the above problems, the present invention has the following features.

  1. A lower mold having a first molding surface for receiving molten glass; and an upper mold having a second molding surface for pressing the molten glass between the first molding surface and the molten glass. In a glass substrate molding die for producing a glass substrate used for an information recording medium by press molding, at least one of the first molding surface and the second molding surface is a convex surface, and the molten glass is A glass substrate molding die, wherein a gap amount between the first molding surface and the second molding surface at the time of pressurization is minimized at a position which is a central portion of the glass substrate.

  2. 2. The mold for molding a glass substrate according to 1 above, wherein a difference between the gap amount at a position serving as the outermost peripheral portion of the glass substrate and the gap amount at a position serving as a central portion is 3 μm to 100 μm. .

  3. Glass substrate molding comprising a lower mold having a first molding surface for receiving molten glass and an upper mold having a second molding surface for pressing the molten glass between the first molding surfaces In the manufacturing method of the glass substrate which manufactures the glass substrate used for an information recording medium using the metal mold | die, the molten glass supply process which supplies a molten glass to the 1st shaping | molding surface which the said lower mold has, and said 1st shaping | molding A pressing step for obtaining a glass substrate by cooling the molten glass while pressing the molten glass on the surface and the second molding surface; and after the pressing step, releasing the pressure on the glass substrate to perform mold opening A mold release step, wherein at least one of the first molding surface and the second molding surface is a convex surface, and the first molding surface and the second molding at the time of pressurizing the molten glass. The amount of gap with the surface becomes the center of the glass substrate. Method for producing a glass substrate, characterized in that the minimum position.

  4). 4. The method for producing a glass substrate according to 3 above, wherein a difference between the gap amount at a position serving as the outermost peripheral portion of the glass substrate and the gap amount at a position serving as a central portion is 5 μm to 100 μm.

  5. 5. A method for producing a glass substrate for an information recording medium, comprising a step of polishing a glass substrate produced by the method for producing a glass substrate according to 3 or 4 above.

  6). 6. A method for producing an information recording medium, comprising a step of forming a recording layer on the glass substrate for information recording medium produced by the method for producing a glass substrate for information recording medium described in 5 above.

  ADVANTAGE OF THE INVENTION According to this invention, the cooling rate of the center part of molten glass can be accelerated | stimulated, As a result, sticking of a glass substrate can be suppressed. Therefore, in the method for producing a glass substrate used for an information recording medium by press molding molten glass, it is possible to prevent the glass substrate from being cracked or cracked during release.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Glass for glass substrate molding)
FIG. 1 is a view showing an example of a glass substrate molding die of the present invention. The glass substrate molding die 10 has a lower mold 11 having a first molding surface 13 for receiving molten glass and a second molding surface for pressing the molten glass between the first molding surface. An upper mold 12 is provided.

  In the glass substrate molding die 10, the first molding surface 13 of the lower mold 11 is a flat surface, the second molding surface 14 of the upper mold 12 is a convex surface, and the first molding surface 13 at the time of pressurizing molten glass is used. And the second molding surface 14 have a minimum amount (d0) at a position that is the center of the glass substrate. Therefore, it is possible to suppress sticking of the glass substrate due to molding, and it is possible to prevent the glass substrate from being cracked or cracked during release.

  Thus, at least one of the first molding surface 13 and the second molding surface 14 is a convex surface, and the gap amount d between the first molding surface 13 and the second molding surface 14 at the time of pressurizing the molten glass is as follows. The reason why sticking of the glass substrate can be suppressed by using a mold that is minimized at the position of the center of the glass substrate will be described.

  In a method for producing a glass substrate by press molding molten glass, molten glass having a temperature higher than that of the mold is supplied to a mold maintained at a predetermined temperature. The hot molten glass is deformed while being pressed by the upper and lower molds, and simultaneously dissipates heat and solidifies by cooling to form a glass substrate. Most of the heat dissipation at this time is performed from the contact surface with the mold.

  The present inventor has made extensive studies and the glass substrate after cooling and solidification is strongly stuck to the mold because the cooling rate is different between the central part and the peripheral part of the glass substrate, and the central part is delayed and solidified. I found out that it was the cause. FIG. 6 is a cross-sectional view showing a state of the glass substrate 24 when it is press-molded with a conventional mold 40. In the mold 40, the first molding surface 43 formed on the lower mold 41 and the second molding surface 44 formed on the upper mold 42 are both flat, and the first molding point at the time when the molten glass is pressurized is used. The gap amount d between the molding surface 43 and the second molding surface 44 is uniform regardless of the position. In this case, the glass substrate 24 has a higher cooling rate in the peripheral portion than in the central portion, and solidifies first. The amount of heat shrinkage in the thickness direction of the glass substrate after the peripheral portion solidifies first and loses fluidity is greater in the central portion than in the peripheral portion. For this reason, the thickness of the central portion of the glass substrate is thinner than the thickness of the peripheral portion, and a gap 45 is formed between the glass substrate and the mold. The gap 45 causes the glass substrate 24 to be vacuum-sucked, and the glass substrate 24 strongly sticks to the mold.

  In contrast, in the glass substrate molding die 10 of the present invention, the first molding surface 13 formed on the lower mold 11 is a flat surface, and the second molding surface 14 formed on the upper mold 12 is a convex surface. Yes. FIG. 2 is a cross-sectional view showing a state of the glass substrate 26 when press-molding with the glass substrate molding die 10 of the present invention. Although most of the cooling of the molten glass is due to heat radiation from the contact surface with the mold, the cooling rate is affected by the thickness of the glass substrate, and the cooling proceeds faster as the thickness is thinner. In the glass substrate molding die 10, the second molding surface 14 is a convex surface, the first molding surface 13 is a flat surface, and the first molding surface 13 and the second molding surface 14 at the time of pressing the molten glass The gap amount d is minimum (d0) at the position that is the center of the glass substrate. Therefore, the thickness of the central portion of the glass substrate 26 is reduced, and the cooling rate of the central portion can be increased. As a result, the cooling rate of the central portion is equal to or faster than that of the peripheral portion, so that the air gap 45 does not occur as in the case of FIG. 6, and conversely, the glass substrate is separated from the mold in the peripheral portion. It becomes easy and sticking of a glass substrate can be suppressed.

  At least one of the first molding surface 13 and the second molding surface 14 is a convex surface, and the gap amount d at the time of pressurizing the molten glass is such that the gap amount d is minimized at the center portion of the glass substrate. I just need it. The first molding surface 13 may be a flat surface and the second molding surface may be a convex surface. Conversely, the first molding surface 13 may be a convex surface and the second molding surface may be a flat surface. Further, both the first molding surface and the second molding surface may be convex surfaces. Furthermore, either one of the surfaces can be a convex surface, and the other surface can be a more concave concave surface.

  FIG. 3 is a cross-sectional view showing the state of the glass substrates 26a and 26b when the glass substrate forming molds 10a and 10b, which are modifications of the glass substrate forming mold 10 of the present invention, are press-molded. A glass substrate molding die 10a shown in FIG. 3A includes a lower mold 11a and an upper mold 12a, and both the first molding surface 13a and the second molding surface 14a are convex surfaces. The gap amount d is minimum (d0) at the position that is the center of the glass substrate. 3B has a lower mold 11b and an upper mold 12b, the second molding surface 14b is a convex surface, and the first molding surface 13b is gentler than that. It is concave. Also in this case, the gap amount d at the time of pressurizing the molten glass is the minimum (d0) at the position that is the center of the glass substrate.

  From the viewpoint of easy processing of the mold, the convex surface is preferably a spherical shape. However, the shape is not limited to a spherical surface, and may be a conical shape or a parabolic shape as long as the central portion is higher than the peripheral portion. Further, the shape is not limited to a shape whose height changes continuously, but may be a shape whose height changes discontinuously in a staircase pattern.

  The gap amount d between the first molding surface 13 and the second molding surface 14 at the time of pressurizing the molten glass may be minimized at the position that becomes the center of the glass substrate, and the position that becomes the outermost periphery of the glass substrate. There is no particular limitation on the difference between the gap amount (d1) at and the gap amount (d0) at the center position. Actually, the outer diameter and thickness of the glass substrate to be manufactured, the type of glass, the material and temperature of the mold, etc., so that the cooling rate of the central part of the glass substrate is equal to or faster than the peripheral part. What is necessary is just to set suitably according to. Usually, in order to obtain the effect of sufficiently suppressing the sticking, the difference between d1 and d0 is preferably 3 μm or more, more preferably 5 μm or more. On the other hand, when the difference between d1 and d0 exceeds 100 μm, extra time is required for the processing step for polishing the obtained glass substrate to produce a glass substrate for information recording medium having high flatness. There is. From such a viewpoint, the difference between the gap amount (d1) at the position serving as the outermost peripheral portion of the glass substrate and the gap amount (d0) at the position serving as the central portion is preferably 3 μm to 100 μm, and 5 μm to 100 μm. More preferably.

  In the glass substrate molding die 10 shown in FIG. 2, the first molding surface 13 is a flat surface, and the second molding surface 14 is a convex surface. In this case, the height difference (h2) between the position of the outermost peripheral portion of the glass substrate and the position of the central portion on the second molding surface 14 is equal to the difference between d1 and d0. When both the first molding surface 13a and the second molding surface 14a are convex like the glass substrate molding die 10a shown in FIG. 3A, the glass on the first molding surface 13a. The sum (h1 + h2) of the height difference (h1) between the position that becomes the outermost peripheral portion and the position that becomes the central portion of the substrate and the height difference (h2) on the second molding surface 14a is d1 and d0. Is equal to the difference. Further, when the first molding surface 13b is concave and the second molding surface 14b is convex as in the glass substrate molding die 10b shown in FIG. 3B, the height at the second molding surface 14b. Difference (h2) is required to be larger than the height difference (h1) on the first molding surface 13b, and the difference between h2 and h1 (h2−h1) is the difference between d1 and d0. Is equal to In any case, the size of h1 and h2 may be determined so that the difference between d1 and d0 is preferably 3 μm to 100 μm, more preferably 5 μm to 100 μm.

  Most preferably, at least one of the first molding surface 13 and the second molding surface 14 is a convex surface in all regions in contact with the glass substrate. However, the region which is a convex surface does not necessarily need to be the entire region in contact with the glass substrate, and may be a region smaller than the region in contact with the glass substrate as long as the effect of the present invention is obtained. . Usually, a region having a diameter of 70% or more of the diameter of a region in contact with the glass substrate is preferably a convex surface, and a region having a diameter of 80% or more is more preferably a convex surface.

  The glass substrate molding die 10 of the present invention is made of various heat resistant stainless steels, super hard materials mainly composed of tungsten carbide, silicon carbide, silicon nitride, aluminum nitride, carbon, and the like. These materials can be appropriately selected from known materials. In addition, in order to improve heat resistance, oxidation resistance, etc., it is also possible to use a material in which a protective film such as various metals, ceramics, or carbon is formed on the surface of these materials. The lower mold 11 and the upper mold 12 may be made of the same material, or may be made of different materials.

  The glass substrate molding die 10 of the present invention may be a product in which one lower die 11 is paired with one upper die 12, and one or both of them are plural. May be. For example, even if two or more lower molds 11 are combined with one upper mold 12 or two or more upper molds 12 and two or more lower molds 11 are combined. good. Furthermore, you may provide the other member, for example, the outer-diameter regulation member for forming the outer-diameter end surface of a glass substrate.

(Glass substrate manufacturing method)
The method for producing a glass substrate according to the present invention uses a glass substrate molding die 10 having a lower mold having a first molding surface 13 and an upper mold 12 having a second molding surface 14, and a molten glass. In which a molten glass is added to the first molding surface 13 by the molten glass supply step, and the first molding surface 13 and the second molding surface 14 add the molten glass. It has the pressurization process which obtains a glass substrate by cooling while pressing, and the mold release process which releases the pressurization to a glass substrate and performs mold opening after a pressurization process. At least one of the first molding surface 13 and the second molding surface 14 is a convex surface, and the gap amount d between the first molding surface 13 and the second molding surface 14 at the time when the molten glass is pressed in the pressing step. However, it becomes the minimum at the position which becomes the center of the glass substrate.

(Molten glass supply process)
The molten glass supply step is a step of supplying molten glass to the first molding surface 13 of the lower mold 11. FIG. 4 is a schematic diagram showing the lower mold 11, the molten glass 23, and the like in the molten glass supply process. Here, an example in which the first molding surface 13 is a plane is shown. First, the molten glass 23 flows out from the outflow nozzle 21 and is supplied to the lower mold 11 (FIG. 4A). Thereafter, when the molten glass reaches a predetermined amount, the molten glass 23 is cut by the blade 22 and the molten glass 23 is separated (FIG. 4B).

  The lower mold 11 is heated in advance to a predetermined temperature. There is no restriction | limiting in particular in the temperature of the lower mold | type 11, What is necessary is just to determine suitably by the kind of glass, the size of a glass substrate, etc. If the temperature of the lower mold 11 is too low, the flatness of the glass substrate deteriorates, and problems such as generation of wrinkles on the transfer surface occur. On the other hand, if the temperature is set higher than necessary, it is not preferable because fusion with glass occurs or the mold deteriorates significantly. Usually, it is preferable to make it the temperature range of Tg (glass transition point) -200 degreeC of glass to shape | mold to Tg + 100 degreeC.

  There is no restriction | limiting in particular also in the heating means of the lower mold | type 11, It can select suitably from well-known heating means and can be used. For example, a cartridge heater that is used by being embedded inside the lower mold 11, a sheet heater that is used while being in contact with the outside of the lower mold 11, and the like can be used. Moreover, it can also heat using an infrared heating apparatus or a high frequency induction heating apparatus.

(Pressure process)
The pressurizing step is a step of obtaining the glass substrate 26 by cooling the molten glass while applying pressure on the first molding surface 13 and the second molding surface 14.

  This will be described with reference to FIG. The lower mold 11 supplied with the molten glass 23 in the molten glass supply process moves horizontally to a position facing the upper mold 12. Thereafter, the molten glass is pressurized with the first molding surface 13 of the lower mold 11 and the second molding surface 14 of the upper mold 12. The molten glass is cooled and solidified by dissipating heat from the contact surface with the first molding surface 13 and the second molding surface 14, and becomes a glass substrate 26.

  As described above, in the manufacturing method of the present invention, at least one of the first molding surface 13 and the second molding surface 14 is a convex surface, and the first molding surface at the time when the molten glass is pressed in the pressing step. A glass substrate molding die 10 is used in which the gap amount d between the first molding surface 13 and the second molding surface 14 is minimized at a position that is the center of the glass substrate. Therefore, the cooling rate of the central part of the glass substrate 26 is increased, and sticking of the glass substrate can be suppressed. As a result, it is possible to prevent the glass substrate from being cracked or cracked during release.

  The upper mold 12 is heated to a predetermined temperature similarly to the lower mold 11. The heating temperature and heating means are the same as in the case of the lower mold 11 described above. The heating temperature may be the same as or different from the lower mold 11.

  As a pressurizing means for applying a load to the lower mold 11 and the upper mold 12 to pressurize the molten glass, a known pressurizing means can be appropriately selected and used. For example, an air cylinder, a hydraulic cylinder, an electric cylinder using a servo motor, and the like can be given.

(Release process)
The mold release step is a step of releasing the pressurization to the glass substrate after the pressurizing step and performing mold opening. In the production method of the present invention, the glass substrate obtained in the pressurizing step does not strongly stick to the mold, and the occurrence of cracks and cracks in the glass substrate during mold opening is prevented. After the mold opening, the glass substrate may be recovered by a general recovery method such as vacuum suction.

(Method for producing glass substrate for information recording medium)
A glass substrate for an information recording medium can be manufactured by subjecting the glass substrate (blank material) manufactured by the above-described manufacturing method to a polishing process or the like. FIG. 5 is a view showing an example of a glass substrate for information recording medium manufactured by the method for manufacturing a glass substrate for information recording medium of the present invention. FIG. 5A is a perspective view, and FIG. 5B is a cross-sectional view. The information recording medium glass substrate 30 is a disk-shaped glass substrate in which a central hole 33 is formed, and has a main surface 31, an outer peripheral end surface 34, and an inner peripheral end surface 35. Chamfered portions 36 and 37 are formed on the outer peripheral end surface 34 and the inner peripheral end surface 35, respectively.

  A grinding | polishing process is a process of grind | polishing the main surface of the glass substrate (blank material) obtained by press molding, and is a process finally finished to the smoothness requested | required as a glass substrate for information recording media. As a polishing method, a known method used as a method for producing a glass substrate for an information recording medium can be used as it is. For example, a pad is pasted on the opposing surface of two rotatable surface plates placed opposite to each other, a glass substrate is placed between the two pads, and the glass substrate surface is rotated simultaneously with the pad contacting the glass substrate surface. It can carry out by the method of supplying an abrasive | polishing agent to. Further, it is also preferable to perform polishing in a plurality of steps such as a rough polishing step and a precision polishing step by changing the particle size of the abrasive and the type of pad.

  Examples of the abrasive include cerium oxide, zirconium oxide, aluminum oxide, manganese oxide, colloidal silica, and diamond. Among these, it is preferable to use cerium oxide which has high reactivity with glass and can obtain a smooth polished surface in a short time.

  The pad is divided into a hard pad and a soft pad, but can be appropriately selected and used as necessary. Examples of the hard pad include pads made of hard velor, urethane foam, pitch-containing suede, etc., and examples of the soft pad include pads made of suede, velor, etc.

  Moreover, in the manufacturing method of the glass substrate for information recording media of this invention, it is preferable to perform an inner and outer periphery processing process and a lapping process other than the grinding | polishing process which grind | polishes the main surface of a glass substrate. The inner and outer peripheral machining process is a process of drilling the center hole, grinding to ensure the shape and dimensional accuracy of the outer peripheral end face and inner peripheral end face, polishing the inner and outer peripheral end faces, etc. In order to satisfy the flatness, thickness, parallelism, etc. of the surface to be formed, this is a step of lapping before the polishing step. Furthermore, when using chemically strengthened glass or crystallized glass as the material of the glass substrate, a crystal strengthening process in which the glass substrate is immersed in a heated chemical strengthening treatment solution to perform ion exchange, or a crystal to be crystallized by heat treatment. The conversion step or the like can be appropriately performed as necessary. Each process such as the inner and outer peripheral processing step, the lapping step, the chemical strengthening step, and the crystallization step can be performed by a method that is usually used as a method for manufacturing a glass substrate for information recording media.

  In addition, in the manufacturing method of the glass substrate for information recording media of this invention, you may have various processes other than the above. For example, annealing process for heat treatment to relieve internal distortion of the glass substrate, heat shock process for confirming the reliability of the strength of the glass substrate, foreign materials such as abrasives and chemical strengthening treatment liquid remaining on the surface of the glass substrate It may have a cleaning process for removing, various inspection / evaluation processes, and the like.

There is no restriction | limiting in particular in the material of a glass substrate, The material used as a material of the glass substrate for information recording media can be selected suitably, and can be used. Among these, chemically strengthened glass and crystallized glass are preferable because they are excellent in impact resistance and vibration resistance. Examples of glass materials that can be chemically strengthened include soda lime glass mainly composed of SiO ₂ , Na ₂ O, and CaO; SiO ₂ , Al ₂ O ₃ , R ₂ O (R = K, Na, Li). Aluminosilicate glass as main component; borosilicate glass; Li ₂ O—SiO ₂ glass; Li ₂ O—Al ₂ O ₃ —SiO ₂ glass; R′O—Al ₂ O ₃ —SiO ₂ glass (R '= Mg, Ca, Sr, Ba) and the like.

  There is no restriction | limiting in particular also in the magnitude | size of a glass substrate. For example, glass substrates having various sizes such as 2.5 inches, 1.8 inches, 1 inch, and 0.8 inches in outer diameter can be used. Moreover, there is no restriction | limiting also in the thickness of a glass substrate. For example, glass substrates having various thicknesses such as 1 mm, 0.64 mm, and 0.4 mm can be used.

(Method of manufacturing information recording medium)
An information recording medium can be produced by forming at least a recording layer on the glass substrate for information recording medium of the present invention. The recording layer is not particularly limited, and various recording layers utilizing properties such as magnetism, light, and magnetomagnetism can be used. In particular, for the production of an information recording medium (magnetic disk) using the magnetic layer as a recording layer. Is preferred.

  There is no restriction | limiting in particular as a magnetic material used for a magnetic layer, A well-known material can be selected suitably and can be used. Examples thereof include CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, and CoCrPtSiO containing Co as a main component. The magnetic layer may be divided by a nonmagnetic film (for example, Cr, CrMo, CrV, etc.) to have a multilayer structure in which noise is reduced.

As the magnetic layer, in addition to the above-mentioned Co-based material, ferrite or iron - and material of the rare earth-based, Fe, Co, CoFe, magnetic particles such CoNiPt are dispersed in a non-magnetic film made of SiO _2, BN A granular structure can also be used. The magnetic layer may be either an in-plane type or a vertical type.

  As a method for forming the magnetic film, a known method can be used. For example, a sputtering method, an electroless plating method, a spin coating method, and the like can be given.

The magnetic disk may further be provided with an underlayer, a protective layer, a lubricating layer, and the like as necessary. Any of these layers can be used by appropriately selecting a known material. Examples of the material for the underlayer include Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. Examples of the material for the protective layer include Cr, Cr alloy, C, ZrO ₂ , and SiO ₂ . Moreover, as a lubrication layer, the thing etc. which apply | coated the liquid lubricant which consists of perfluoro polyether (PFPE) etc., and heat-processed as needed are mentioned, for example.

(Examples 1-5)
As the mold, a glass substrate molding mold 10 was prepared in which the first molding surface 13 of the lower mold 11 was flat and the second molding surface 14 of the upper mold 12 was convex (spherical). As shown in Table 1, the upper mold 12 has a height difference (h2) between a position (the diameter of 70 mm in diameter) and a center position on the second molding surface 14 as the outermost peripheral portion of the glass substrate. Different upper molds 12 were prepared. When each upper mold 12 is used, the difference in the gap amount d between the position that becomes the outermost peripheral portion and the position that becomes the central portion of the glass substrate is 3 μm (Example 1), 5 μm (Example 2), and 10 μm. (Example 3), 50 μm (Example 4), and 100 μm (Example 5). The material of the upper mold 12 and the lower mold 11 was SUS310S.

  Both the lower mold 11 and the upper mold 12 are heated to 400 ° C., and molten glass is supplied to the first molding surface 13 of the lower mold 11, and then press-molded with the second molding surface 14 of the upper mold 12. went. As the glass material, borosilicate glass was used. After pressurizing for 3 seconds, the mold was opened to recover the glass substrate. This was repeated 1000 times for each mold, and the presence or absence of cracks in the obtained glass substrate was confirmed by visual inspection. Here, the case where the occurrence of cracks was less than 20 out of 1000 sheets was judged as good (determination: ◯), and the case where it was less than 10 was judged as very good (determination: ◎). Moreover, the case where the occurrence of cracks was 20 or more was regarded as problematic (judgment: x). The glass substrate had an outer diameter of 70 mm and a thickness of 1 mm.

  The results are shown in Table 1. In all cases, the occurrence of cracks was less than 20 sheets, which was good. In particular, when the difference in the gap amount d between the position that becomes the outermost peripheral portion and the position that becomes the central portion of the glass substrate is 5 μm or more (Examples 2 to 5), the occurrence of cracks is very good at less than 10 sheets. there were.

(Comparative Example 1)
As the upper mold 12, a glass substrate was molded and evaluated in the same manner as in Examples 1 to 5, except that the second molding surface 14 was flat. The results are also shown in Table 1.

  In the case of Comparative Example 1, cracks occurred in all glass substrates from the start of molding to the 20th molding, and a good glass substrate could not be obtained. The experiment was stopped at that time.

(Examples 6 to 9)
The second molding surface 14 of the upper mold 12 is a convex surface (spherical surface), and the height difference (h2) between the position that becomes the outermost peripheral portion of the glass substrate (position with a diameter of 70 mm) and the position that becomes the central portion is 20 μm. I prepared one. As shown in Table 2, four types of lower molds 11 were prepared in which the first molding surface 13 was a concave surface (spherical surface), a flat surface, and a convex surface (two types of spherical surfaces). Table 2 shows the difference in height (h1) between the position of the outermost peripheral part of the glass substrate (position of diameter φ70 mm) and the position of the central part on the first molding surface 13 of each lower mold 11. It is. In each case, the difference in the gap amount d between the outermost peripheral part and the central part of the glass substrate is 10 μm (Example 6), 20 μm (Example 7), 30 μm (Example 8), 40 μm (Example 9). It becomes.

  Using these molds, the glass substrate was molded and evaluated in the same manner as in Examples 1-5. The results are shown in Table 2. In any combination, the occurrence of cracks was very good at less than 10 sheets.

(Comparative Example 2)
As the lower mold 11, the first molding surface 13 is a concave surface (spherical surface), and the height difference (h1) between the position that becomes the outermost peripheral portion of the glass substrate (position with a diameter of 70 mm) and the position that becomes the central portion is 20 μm. (The center is 20 μm lower). The upper mold 12 was the same as in Examples 6-9. In this case, the gap amount d between the first molding surface 13 and the second molding surface 14 is uniform, and there is no difference in the gap amount d between the outermost peripheral portion and the central portion of the glass substrate. Using such a mold, the glass substrate was molded and evaluated in the same manner as in Examples 6 to 9. The results are also shown in Table 2.

  In the case of Comparative Example 2, cracks occurred in all the glass substrates from the start of molding to the 20th molding, and a good glass substrate could not be obtained. The experiment was stopped at that time.

It is a figure which shows the example of the metal substrate shaping die of this invention. It is sectional drawing which shows the state of the glass substrate 26 at the time of press-molding with the glass substrate shaping die 10 of this invention. It is sectional drawing which shows the state of glass substrate 26a, 26b at the time of press-molding with the glass substrate shaping | molding metal mold | die 10a, 10b which is a modification of the glass substrate shaping die 10 of this invention. It is a schematic diagram which shows the lower mold | type, a molten glass, etc. in a molten glass supply process. It is a figure which shows one example of the glass substrate for information recording media manufactured by the manufacturing method of the glass substrate for information recording media of this invention. It is sectional drawing which shows the state of the glass substrate 24 at the time of press-molding with the conventional metal mold | die 40. FIG.

Explanation of symbols

10, 10a, 10b Glass substrate molding die 11, 11a, 11b Lower mold 12, 12a, 12b Upper mold 13, 13a, 13b First molding surface 14, 14a, 14b Second molding surface 23 Molten glass 26, 26a, 26b Glass substrate 30 Glass substrate for information recording medium d Gap amount d0 Gap amount at the center portion of the glass substrate d1 Gap amount at the position of the outermost peripheral portion of the glass substrate

Claims (6)

A lower mold having a first molding surface for receiving molten glass;
An upper mold having a second molding surface for pressurizing the molten glass with the first molding surface;
In a glass substrate molding die for producing a glass substrate used for an information recording medium by press molding the molten glass,
At least one of the first molding surface and the second molding surface is a convex surface,
A glass substrate molding metal, wherein a gap amount between the first molding surface and the second molding surface at the time of pressurizing the molten glass is minimized at a position which is a central portion of the glass substrate. Type.   2. The glass substrate molding gold according to claim 1, wherein a difference between the gap amount at a position that is the outermost peripheral portion of the glass substrate and the gap amount at a position that is a central portion is 3 μm to 100 μm. Type. A lower mold having a first molding surface for receiving molten glass;
A glass substrate used for an information recording medium is manufactured using a glass substrate molding die having an upper mold having a second molding surface for pressing the molten glass between the first molding surface and the first molding surface. In the method for producing a glass substrate,
A molten glass supply step of supplying molten glass to the first molding surface of the lower mold;
A pressurizing step of obtaining a glass substrate by cooling while pressing the molten glass on the first molding surface and the second molding surface;
After the pressurizing step, having a mold release step of releasing the pressurization to the glass substrate and performing mold opening,
At least one of the first molding surface and the second molding surface is a convex surface,
A method for producing a glass substrate, wherein a gap amount between the first molding surface and the second molding surface at the time of pressurizing the molten glass is minimized at a position which is a central portion of the glass substrate. .   The method for producing a glass substrate according to claim 3, wherein a difference between the gap amount at a position that is the outermost peripheral portion of the glass substrate and the gap amount at a position that is a central portion is 5 μm to 100 μm. .   A method for producing a glass substrate for an information recording medium, comprising the step of polishing a glass substrate produced by the method for producing a glass substrate according to claim 3.   A method for producing an information recording medium, comprising the step of forming a recording layer on the glass substrate for information recording medium produced by the method for producing a glass substrate for information recording medium according to claim 5.

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